1. Field of the Invention
This invention relates generally to the field of touch panel design, and more particularly to the design of a resistive matrix touch panel.
2. Description of the Related Art
It's been a high priority for many electronics manufacturers to offer user interfaces that are powerful yet simple to use, while remaining highly reliable. Some of the more popular interfaces have been touchscreens and touchpads. Touchscreens and touchpads can typically detect the location of touches within the display/pad area, allowing the display/pad to be used as an input device, and in the case of touchscreens, making it possible for the user to directly interact with the display's content. Such displays/pads can be attached to computers, and have become more and more prevalent in recent personal digital assistants (PDAs), laptop computers, and satellite navigation and mobile phone devices, making these devices more user-friendly and effective.
Touchscreens/touchpads can be designed based on different sensing principles. The most widely used touchpads or touch panels (TPs) are designed based on capacitive or resistive sensing principles. Capacitive touchscreens/touchpads may feature a panel coated with a material that conducts a continuous electrical current across the sensor, which exhibits a precisely controlled field of stored electrons in both the horizontal and vertical axes to achieve capacitance. When the sensor's normal capacitive field (considered its reference state) is altered by another capacitive field, for example someone's finger, electronic circuits measure the resultant distortion in the characteristics of the reference field, and send the information about the event to a controller for processing. Capacitive sensors can either be touched with a bare finger or with a conductive device being held by a bare hand.
Resistive touchscreens are typically composed of two flexible sheets coated with a resistive material, and separated by an air gap or microdots. Most commonly, resistive TPs are constructed using one of two different types of metallic layers, referred to as matrix and analogue, respectively. In a matrix TP, striped electrodes are configured to face each other on substrates such as glass or plastic. In Analogue TPs, transparent electrodes without any patterning are configured to face each other. When contact is made with the surface of the TP, the two sheets are pressed together, causing the horizontal and vertical lines present on the two sheets to be pushed together and register the precise location of the touch. Resistive TPs provide accurate touch control, and because they are responsive to surface pressure, contact can be made with nearly any object (e.g. a finger, stylus/pen, etc.). Resistive sensing technology is therefore considered to be “passive”.
For example, during operation of a four-wire TP, a uniform, unidirectional voltage gradient is applied to one of the sheets, and when the two sheets are pressed together, the second sheet measures the voltage as distance along the first sheet, to provide one of two (x,y) coordinates. Once the first coordinate has been acquired, the voltage gradient is applied to the second sheet to ascertain the other coordinate to register the exact touch location as contact is made. Because resistive TP technology works well with almost any pointer object, and can be operated with covered as well as bare fingers, they can oftentimes be more desirable than a capacitive TPs, which have to be operated with a capacitive pointer, such as a bare finger, for example. The matrix touch panel relies on much the same technology, with the difference that one sheet is patterned in the “X” direction, while the other sheet is patterned in the “Y” direction. The “Y” patterned films are referred to as column or driver tracks, the “X” patterned film is referred to as the row or receiver tracks.
Due to the sensing technology used in their design, resistive TPs can also support multi-touch input. However, most present day matrix touch panels reduce the useable signal by as much as 50× because of the termination values and techniques used. As a result, the RTL (register transfer language) and firmware that are required to extract the signal and produce usable multi-touch capability are limited. Also, each application has to be tuned individually, since the impedance of the TP is driven by optical, not electrical performance (as opposed to capacitive touch sensing). Current solutions use a termination scheme that results in approximately 70%-99% attenuation of the signal. Also, the “RC” network varies over the TP, and tuning resistors are used to slow all responses down, intentionally disposing of otherwise available portions of the signal through the termination schemes.
Many other problems and disadvantages of the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.